1. Field of the Invention
This invention relates to a tanker ship for carrying low temperature liquefied gases such as liquefied natural gas and, more particularly, an improvement regarding the structure of a secondary barrier wall which temporarily prevents leakage of liquefied gases which may occur at an inner membraneous vessel of a low temperature liquefied gas tank incorporated in the tanker ship.
2. Description of the Prior Art
Generally, in a tanker ship for carrying liquefied gases of a relatively moderate cold temperature such as, for example, down to minus 50.degree. centigrade, a hull of the ship itself can serve as the aforementioned secondary barrier wall. However, in a tanker ship which carries liquefied gases of much lower temperatures, an independent secondary barrier wall other than the hull is required. In this case, if the secondary barrier wall is provided to cover the entire body of the inner vessel, it requires a substantial amount of material and manufacturing causing, as a result, a substantial increase in the construction cost of a tanker ship.
In view of the above drawback, it has been proposed to provide a secondary barrier wall which covers only bottom and lower portions of side walls of an inner membraneous vessel from the outside thereof, said secondary barrier wall being extended over a corresponding inner surface portion of a heat insulating layer provided between an outer shell or hull and the inner membraneous vessel. However, this structure is bound with a drawback that air tightness of the secondary barrier wall becomes very difficult to test.